Management system and methods of managing time-division duplex (tdd) transmission over copper

ABSTRACT

Time division duplex transmission over copper physical channels is managed. In one example, upstream time slots for upstream transmission in a first physical channel are scheduled. Downstream time slots for downstream transmission in a second physical channel are scheduled. Transmission in the upstream time slots is substantially not simultaneous with transmission in the downstream time slots.

FIELD

The present description relates to the field of data transmission inchannels subject to crosstalk and, in particular, to scheduling timeslot allocations for such channels.

BACKGROUND

TDD (Time Division Duplex) systems transmit downstream (network tosubscriber) data and upstream (subscriber to network) data in distincttime slots of the same physical channel. Additionally, there is often asmall guard-time between distinct time slots to ensure that data doesnot overlap. One new TDD system is called ‘G.fast,’ which is currentlyin the process of standardization by the ITU-T (InternationalTelecommunication Union—Telecommunication Standardization Sector).G.fast is to transmit over relatively short (<250 m) copper telephoneloops and premises wiring.

FIG. 1 is a diagram of slots on a horizontal time axis for a classic TDDsystem, alternately transmitting downstream from the network toward thesubscriber and upstream from the subscriber toward the network indifferent Down and Up TDD time slots. There is a downstream slot 12, andan upstream slot 14. This is followed by another downstream slot 16 andthen an upstream slot 18. The cycle is repeated along the horizontaltime axis. The “asymmetry ratio” is the ratio of the size of the Downslot compared to the size of the Up slot. There is usually also a smallguard-time (not shown) between each time slot. Each repetition of thetwo slots may be referred to as a frame. Alternatively, a frame may havemultiple repetitions of the two slots.

To reduce power consumption and interference on nearby lines, a powersaving TDD system is shown in FIG. 2. FIG. 2 is a diagram of slots on ahorizontal axis for the power saving TDD system. Broadband datacommunication systems are often idle or highly underutilized, andcurrent practice is generally to send idle codes at full power whenthere is no data traffic. A power saving alternative is to suppresstransmission when there is no user data traffic. As shown in FIG. 2,there are two frames 21, 22, TDD frame₁, TDD frame₂, each having adownstream slot, 23, 27, followed by an upstream slot, 25, 29. Inaddition, a portion of the downstream slot, in this case the laterportion, is an off portion, D_off 24, 28, during which transmission issuppressed. During the off portion, neither data nor idle bits are sent.Similarly the upstream slot, Up, has an off portion U_off 26, 30 at theend of each slot, during which neither data, nor idle bits are sent.Sending no power, during off times “D_off” and “U_off” can providesignificant power savings. “D_off” and “U_off” may also be combined intoa single off portion.

In many TDD systems, there are multiple physical channels. If thesechannels are close together in location and overlap in frequency, thenthey may interfere with each other. FIG. 3 is a diagram of a TDD systemwith two channels 31, 32. In this example, each channel uses a twistedpair of copper cables and both channels are in the same cable or cablebinder. As illustrated in FIG. 3, systems transmitting in multi-paircopper cables can generate crosstalk into each other, Near-End Crosstalk(NEXT) 33 and Far-End Crosstalk (FEXT) 34 are generated by each channeland directed at least in part into the nearby channel.

Each channel is connected between a network-end Transmission Unit-Office(TU-O) 35, 36 and a subscriber-end Transmission Unit-Remote (TU-R)transceiver 37, 38. While each channel is shown as connecting adifferent TU-O to its own TU-R, a single TU-O can connect to a singleTU-R using both of the two channels. This allows more data to be sent tothe one TU-R. A single TU-O may also connect to multiple TU-Rs, which issometimes called “bonding.”

NEXT can be very powerful and debilitate high speed transmissions. ADSL(Asymmetric Digital Subscriber Line) and VDSL (Very high bit rateDigital Subscriber Line) use Frequency-Division Multiplexing (FDM) toavoid self-NEXT. Self-NEXT 33 is the crosstalk that is created intoneighboring channels as shown in FIG. 3.

SUMMARY

In one example, a method for managing multiple physical channels in adata communications system that are subject to crosstalk is described.The method includes scheduling time slot allocations for the physicalchannels so that upstream transmissions do not occur at the same time asdownstream transmissions. In another example, the method is implementedby a machine operating on a machine-readable medium having storedinstructions. In another example, a time slot management system managesmultiple physical channels in a data communications system that aresubject to crosstalk. The system has a process for determining time slotallocations for the physical channels so that upstream transmissions donot occur at the same time as downstream transmissions and acommunications interface to make assignments to transmitters of thephysical channels.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Embodiments are illustrated by way of example, and not by way oflimitation, and will be more fully understood with reference to thefollowing detailed description when considered in connection with thefigures in which:

FIG. 1 is a diagram of slots on a horizontal time axis for a classic TDDsystem;

FIG. 2 is a diagram of slots on a horizontal axis for a power saving TDDsystem;

FIG. 3 is a diagram of two related physical channels connected to endnodes in a TDD system;

FIG. 4 is a diagram of slot assignments for two related physicalchannels according to an embodiment of the invention;

FIG. 5 is a diagram of alternative slot assignments for two relatedphysical channels according to an embodiment of the invention;

FIG. 6 is a diagram of further alternative slot assignments for tworelated physical channels according to an embodiment of the invention;

FIG. 7 is a diagram of a twisted pair having at least two relatedphysical channels connected between a central office and an end node;

FIG. 8 is a process flow diagram of an example of computing TDD slottimes and off times according to an embodiment of the invention;

FIG. 9 is a process flow diagram of computing start and end times oftime slots according to an embodiment of the invention;

FIG. 10 is a diagram of multiple TDD groups that have crosstalk couplingbetween some of their lines including autonomous TDD managementaccording to an embodiment of the invention;

FIG. 11 is a process flow diagram of another example of computing TDDslot times according to an embodiment of the invention; and

FIG. 12 is a block diagram of a TDD management system according to anembodiment of the invention.

DETAILED DESCRIPTION

Embodiments of the invention may provide a management system for systemsthat transmit over wires using Time-Division Duplex (TDD). Themanagement system receives input data about service levels, traffic,power and other requirements. It then determines an assignment of TDDtime slots, off times, and asymmetry; for optimal performance, minimaltraffic delays, and minimal power usage. The TDD frames are flexible andneed not follow a fixed pattern.

One way to avoid self-NEXT is to synchronize the transmissions on thetwo lines so that one line does not transmit downstream while anotherline transmits upstream. This is particularly important with TDD systemsthat have channels that use the same multi-pair cable binder.

FIG. 4. is a diagram showing TDD frames, frame₁, frame₂, on twodifferent channels, Line₁, Line₂, which are close enough to cause NEXT41, 42 in the other line. The frames are shown as aligned across ahorizontal time axis. Each frame for each channel has a downstream slot,43-1, 43-2, 44-1, 44-2, and an upstream slot, 45-1, 46-2, 45-2, 46-2.Even though the TDD frames are aligned, in this case the slots are not.Line₁, the upper line, is transmitting predominately in the upstreamdirection while Line₂ is transmitting predominately in the downstreamdirection. The downstream and upstream misalignment causes NEXT 41, 42in the nearby line. As shown, the Line₁ frame₁ upstream slot 45-1 beginsbefore the Line₂ frame₂ downstream slot 43-2 completes. During thisoverlap, NEXT 41 is much higher. After the Line₂ frame₂ downstream slot43-2 ends and the upstream slot 45-2 begin, NEXT 41 is greatly reduced.A similar overlap occurs in frame₂.

One way of avoiding NEXT is to align all the TDD frames, the downstreamand upstream time slots, and the off times, as shown for example in FIG.5. As in FIG. 4, the frame structure frame₁, frame₂ for two nearbychannels Line₁, Line₂ are shown aligned on a horizontal time axis. Boththe upper line, Line₁ and the lower line, Line₂, have downstream 53-1,54-1, 53-2, 54-2 and upstream slots 55-1, 56-1, 55-2, 56-2 which arealigned with respect to time. As a result, the two channels will becarrying downstream data at the same time and upstream data at the sametime. Since no downstream transmission occurs during an upstreamtransmission, NEXT is minimized.

In addition, the two frames also have off portions, D_off 57-1, 58-1,57-2, 58-2, in each downstream slot of each frame and U_off 51-1, 52-1,51-2, 52-2 in each upstream slot of each frame. Part of each upstreamand each downstream slot is shown as being off to save power. The offportions are also aligned.

A more flexible way of avoiding NEXT, instead of enforcing perfectalignment of each slot in each frame as in FIG. 5, is to enforcesufficient alignment to avoid transmitting upstream and downstream atthe same time on any line. This has the advantage that one line cantransmit more data than other lines if it has high demand, while theother lines can be quiet and save power. Further, the frame times can bevaried. This, however, has the disadvantage that it requires a highlevel of control and coordination. FIG. 6 shows an example of this.

FIG. 6 shows two channels an upper, Line₁, and a lower, Line₂, alignedon a horizontal time axis. The downstream 63-1, 64-1, 63-2, 64-2 andupstream 65-1, 66-1, 65-2, 66-2 portions of these two channels arealigned as in FIG. 5. However, the off portions, the downstream offportions D_off 67-1, 68-1, 67-2, 68-2, and U_off, the upstream offportions 61-1, 66-1, 61-2, 66-2 are not aligned. In order to eliminateNEXT, the off portions do not need to be aligned. When a channel is off,then it is not generating any interference. Each of these off periods donot need to be aligned for all lines in all TDD groups of a multiplechannel binder. Embodiments of the invention help to control the offperiods and determine how to adapt the off periods for each channel toavoid NEXT and to minimize power usage.

A further method of mitigating NEXT is to employ active NEXTcancellation at the network end of the lines, where the TU-Os arelocated. This is generally feasible among TU-Os that are in the sameequipment chassis, or at least in the same location. In such a case,transmitted data signals, received upstream signals plus NEXT, and theassociated error signals are available to a cancellation system orfilter, which subtracts estimates of the NEXT from the received signalsin real-time. The NEXT canceller may have a zero-forcing structure, aminimum-mean square error (MMSE) structure, a decision-feedbackequalizer (DFE) structure, or any other cancellation filter structure.The cancellation coefficients may be calculated at start-up, and may beadapted using error signals while the lines are active.

NEXT cancellation eliminates most of the NEXT from downstream signalsinto upstream signals, allowing some overlap between downstream andupstream time slots. NEXT from upstream signals into downstream signalsoccurs primarily at the subscriber ends of the lines where the upstreamsignals are strongest. The amplitude of this NEXT may be low enough tobe ignored due to the attenuation that occurs on drop and inside wires.Transmitting upstream and downstream simultaneously in the samefrequencies is known as full-duplex operation, and generally alsorequires line hybrids and echo cancellers. Compatibility with VDSL2 maybe enabled by using NEXT cancellation at the TU-O end of the lines andby not allowing upstream transmission in the VDSL2 downstream frequencybands unless the NEXT is low at the subscriber end of the lines.Different bit loadings may be used when transmitting upstream anddownstream simultaneously, and when transmitting in only one direction.

With NEXT cancellation, management of the TDD system proceeds asdescribed elsewhere here, except that some overlap between downstreamand upstream time slots may be allowed in some cases or in some timeslots. The combination of time slot and frequency-band allocations canbe dynamically adjusted for each environment.

Several network-end transmission units (TU-O) are often in a singleaccess node. One example of a single access node is a Digital SubscriberLine Access Multiplexer (DSLAM). Referring to FIG. 7, a central office(CO) or exchange 71 is coupled through a feeder 72 to one or morecrossboxes or splice points 73, although only one is shown. The crossboxis coupled through a distribution line 74 to one or more drop wireinterfaces 75, although only one is shown. The drop wire interface iscoupled though one or more drops or drop wires 76 to one or more TU-Rs77, although only one is shown. Depending on the system implementation,the crossbox 73 may be replaced with or in the form of, for example, afeeder distribution interface (FDI), a serving area interface (SAI), ajunction wire interface (JWI), or a sub-loop distribution frame (SDF).The drop wire interface 75 may be replaced with or in the form of adistribution terminal or a deployment point (dP).

The access node or DSLAM (not shown) can be located in the distributionterminal or it can be located somewhere else in the distribution plant,and usually it is fed with optical fiber from the Central Office (CO) orexchange. Downstream of the access node, toward the TU-Rs, crosstalk maybe only between lines from a single access node, or there may becrosstalk between lines from multiple access nodes. A set of lines usingTDD that all originate at the same access node will be referred toherein as a TDD group.

The invention may be embodied by a TDD management system thatcoordinates the TDD slot times and the off times of different channelsto maximize the transmission of user data traffic while minimizingpower. On and off times may be selected to ensure there is nopossibility of creating NEXT between lines in a TDD group, or betweenlines in different TDD groups that have crosstalk coupling into eachother. The on and off times may also be chosen to maximize trafficthroughput to meet user demands, and to also minimize power consumptionby being off when possible.

The TDD management system receives input on the traffic levels, traffictypes, and traffic patterns that should be provided on the lines underits control. This input may include one or more of the following:

a) static (time-invariant) data about service subscription levels andtheir traffic requirements, e.g. a “traffic descriptor;

b) service layer information from a policy manager which provideshigh-level estimates of data rate requirements based on servicerequests;

c) data on the behavior of different traffic types, different users,e.g. bit rate variations, traffic behavior, or burstiness;

d) time series data from long term traffic monitoring which is analyzedto determine the traffic demands as a function of time-of-day ortime-of-week;

e) instantaneous feedback based on current traffic demands or queuelengths (Queue lengths or traffic requests can be sent from the customerend up to the network-end for input to the TDD management system);

f) upstream and downstream traffic asymmetry patterns; and

g) traffic requests or reports.

The traffic can further be classified according to priority level,service type, QoS (Quality of Service), tagging, stream type, protocoltype, etc., and this classification information can be input to TDDscheduling algorithms.

The TDD management system uses this input to calculate TDD slot timesand off times. The slot times are arranged in such a way as to avoid orreduce NEXT when possible, for example as shown in FIG. 6. Ideally, notwo lines that have significant crosstalk coupling into each other cantransmit upstream and downstream at the same time. The slot times andoff times may also be calculated to satisfy the traffic requested bysubscribers, and can further minimize power usage by maximizing offtimes.

FIG. 8 is a process flow diagram of an example of computing TDD slottimes and off times as described above. At 800, the bandwidthrequirements or requests of the users are received, collected,calculated, or measured. The information may be based on the inputreceived by the TDD management system as described above. Thisinformation may include any number of different factors including thetype of traffic (for example fixed, variable), and the amount ofbandwidth requested (for example in Bytes or microseconds). Thebandwidth requirements of some users may be fixed over time, such as forstreaming video, while the bandwidth of others may vary.

At 810, an aggregation function (maximum, average, etc.) of the userbandwidth requests for downstream and upstream is calculated fordifferent types of traffic. For example, the function could be themaximum of all users' downstream fixed bandwidth requests. Furtherexamples are provided in the next section.

At 820, the next downstream, upstream and off time time slot periods arecalculated based on the calculated aggregation function. For example,the next downstream time slot duration could be equal to the sum of themaximum downstream requests for all types of traffic. In such a case,for instance it is guaranteed that no user's bandwidth request wouldexceed the time slot duration allocated for that type of traffic.Further examples are provided below.

At 830, each user's downstream, upstream and off time time slot periodsare assigned and then, if need be, they are adjusted. If the conditionsof previous operations are properly satisfied, then each user should beable to receive its requested bandwidth, given limitations orrequirements of its traffic type. It is also possible that, for example,the assignments could provide excess bandwidth for certain users. Insuch cases, adjustments may be made to utilize this excess capacity, forexample by assigning variable bit rate traffic to excess fixed bandwidthtime slots, or by assigning off time for power savings. Further examplesare provided below. The assignment of time slots may be internal to atransceiver, or it may be transmitted from the TDD management systemdown to the transceiver.

The following provides an example of the process above, for assigningbandwidth at a single access node with mixtures of delay-sensitive fixedbandwidth assignments (e.g., video, voice) and delay-insensitivereal-time bandwidth assignments (e.g., data). This example assumesbandwidth requests were converted into time slot requests inmicroseconds. If user i has a data rate of Z Mbps, and is requesting Bbits of traffic, the request equals B/Z microseconds in the next frame.

1) The receive, collect, measure, or calculate operation at 800 may beperformed as receiving bandwidth request data input for each user. Thisdata may, for example, include any of the following:

a) Fixed upstream bandwidth requests, e.g. UXi microseconds dedicatedfor each user i;

b) Real-time upstream bandwidth requests, e.g. UYi microseconds in thenext time slot for user i;

c) Fixed downstream bandwidth requests, e.g. DXi microseconds dedicatedfor each user i; and

d) Real-time downstream bandwidth requests, e.g. DYi microseconds in thenext time slot for user i.

2) The calculation of the aggregated function at 810 may be performed inseveral steps. First, the maximum requested bandwidth of each type inthe next frame is calculated. These can be defined, for example, asfollows:

a) Maximum fixed upstream bandwidth request e.g. MaxUX=max over i (UXi);

b) Maximum real-time upstream bandwidth request e.g. MaxUY=max over i(UYi);

c) Maximum fixed downstream bandwidth request e.g. MaxDX=max over i(DXi); and

d) Maximum real-time downstream bandwidth request e.g. MaxDY=max over i(DYi)

3) The time duration of the next frame may be named TF. The time slotdurations can be determined at 820 using different criteria depending onthe particular subscriber and system architecture circumstances. Someexamples are provided below, where it is assumed that fixed bandwidthrequests have strict priority over real-time bandwidth requests.

4) If TF>=MaxUX+MaxUY+MaxDX+MaxDY, then the next upstream time slotduration is MaxUX+MaxUY, the next downstream time slot duration isMaxDX+MaxDY, and the off time in the next TDD frame isTF−(MaxUX+MaxUY+MaxDX+MaxDY).

5) Otherwise, if MaxUX+MaxUY+MaxDX+MaxDY>TF>MaxUX+MaxDX, then the fixedbandwidth requests will be completely satisfied and the real-timebandwidth requests will be partially satisfied. One way of doing this isto divide the real-time bandwidth proportional to the maximum requestedreal-time bandwidth so that the next upstream time slot duration is

MaxUX+(TF−MaxUX−MaxDX)*(MaxUY/(MaxUY+MaxDY),

the next downstream time slot duration is

MaxDX+(TF−MaxUX−MaxDX)*(MaxDY/(MaxUY+MaxDY),

and there is no off time in the next time slot.

6) Otherwise, if TF=MaxUX+MaxDX, then the next upstream time slotduration is MaxUX and the next downstream time slot duration is MaxDX.

7) Otherwise, if MaxUX+MaxDX>TF, then the fixed bandwidth requests arepartially satisfied and the real-time bandwidth requests are notsatisfied at all. One way of doing this is to divide the fixed bandwidthproportional to the maximum requested fixed bandwidth so that the nextupstream time slot duration is TF*(MaxUX/(MaxUX+MaxDX)), the nextdownstream time slot duration is TF*(MaxDX/(MaxUX+MaxDX)), and there isno off time in the next time slot.

8) Having calculated the functions and the time slot durations, theoperations at 830 are performed: assign and adjust each user'sdownstream, upstream and off time time slot period.

There are many variations to the example process described above,depending on the particular application and system architecture, forexample the bandwidth may be divided proportional to average upstreamand downstream requests instead of maximum, or the bandwidth may simplybe split in half, or the bandwidth may be divided along a sliding windowthat accounts for bandwidth requests in multiple time slots, or thebandwidth may be assigned according to a fairness criteria, or thebandwidth may be assigned according to subscription level, etc. Theprocesses may also be extended to more than two different traffic types.The process may operate on multiple TDD frames at a time.

In the example of using the maximum requested bandwidth as describedabove, the time slot dedicated to one or more users could exceed therequired bandwidth requested by those users. In some cases, the requiredbandwidth for a user could be significantly less than the assigned timeslot. For example, MaxUX+MaxUY could be much larger than the UXi+UYi orMaxDX+MaxDY could be much larger than DXi+DYi for a specific user i. Insuch cases, the adjustment stated as step 7 above can be utilized.

As one example, the extra bandwidth may be utilized for either savingpower or improving latency or some combination of both. The TDDmanagement, as an example may extend the off period for those users, toreduce their power consumption. Alternatively, the TDD management systemmay accommodate the available extra bandwidth to be used for variableupstream or downstream traffic for those users to allow newly arrivingtraffic to be transmitted immediately. Conversely, when using theaverage requested bandwidth in the above algorithm, some user requestsmight not get satisfied. For example, the fixed bandwidth requests couldbe partially satisfied. In such cases, steps 5-7 of the above 8-stepprocess for calculating an aggregate function could be modified, whereinstead of Max; the Average function is used. Other functions mayalternatively be used to suit different implementations and differenttraffic management goals.

After the time slot durations are calculated, the start and end times ofeach time slot in the next TDD frame are calculated. This may be asimple assignment anchored at a fixed time such as the beginning or endof a TDD frame. Or it may involve a more involved solution, such as aniterative solution. FIG. 9 is a process flow diagram of an example ofcomputing the start and end times of each time slot in a next orsubsequent TDD frame.

At 900, the next downstream (DS) time slot, the next upstream (US) timeslot, and the next off time locations are assigned to arbitrarylocations in the next TDD frame.

At 910, it is checked whether the downstream time slot is overlappingwith another upstream time slot, or vice versa, whether the upstreamtime slot is overlapping with another downstream time slot. If there isno overlap, then the allocations in step 900 are accepted, and nofurther action is needed.

If there is an overlap, then at 920, the entire downstream time slotassignment or the entire upstream time slot assignment is moved forwardor backward in time, by a predetermined amount or by a random amount.The choice of DS or US is based on whether the overlapping time slot isa DS slot or a US slot from 910.

After this adjustment, the operations at 910 are repeated, and if thereare no more overlaps, then no further action is required. However, ifthere still is an overlap, either with the downstream time slot or withthe upstream time slot, then the operations at 920 are repeated. Ifafter the adjustments the non-overlapping conditions cannot be met, thenthe DS or the US time slot durations are decreased (depending on whichone had the overlapping issue), and the initial assignment at 900 isrepeated.

A more specific example of the operations in the process flow diagram ofFIG. 9 is provided below. As in FIG. 9, this is an example of the aboveprocess for computing the start and end times of each time slot in anext TDD frame. In the following example it is assumed that the previousprocess of FIG. 8 has already been performed, and therefore the nextdownstream time slot DS duration, the next upstream time slot USduration, and the next off time D_off, U_off duration, have already beendetermined.

1) As an example of the operations at 900, assign the next downstreamtime slot, the next upstream time slot, and the next off time(s) toarbitrary locations in the next TDD frame. For example, the next TDDframe may begin with the downstream time slot, then have the next slotbe downstream off time D_off, then have the upstream time slot, and thenhave the next upstream slot be upstream off time U_off. Alternately, theoff time may be contiguous and in the beginning, middle, or end of theTDD frame.

2) If the downstream time slot does not overlap with any other upstreamtime slot of any other TDD system that crosstalks into or from this TDDsystem, then the process is finished until the next time the slots areadjusted based on new parameters. This is the test at 910.

3) Otherwise, move the entire downstream time slot assignment by xmicroseconds either forward or backward in time. This corresponds to theoperation at 920.

4) Repeat step 4, varying x, until the condition of non-overlap in step3 is achieved in the downstream direction. x may be varied randomly orit may vary in predetermined steps.

5) If the condition of step 3 cannot be achieved, then decrease thedownstream time slot duration and repeat steps 1 through 4.

6) If the upstream time slot does not overlap with the downstream timeslot, nor with any other upstream time slot of any other TDD system thatcrosstalks with this TDD system, then the process if finished.

7) Otherwise, move the entire upstream time slot assignment by ymicroseconds either forward or backward in time.

8) Repeat step 7, varying y, until the condition of non-overlap in step6 is achieved in the upstream direction. y may be varied randomly or itmay vary in predetermined steps.

9) If the condition of step 7 cannot be achieved, then decrease theupstream time slot duration and repeat steps 6 through 8.

10) Assign the off time. For example, the off time may be contiguous andin the beginning, middle, or end of the TDD frame; or it may be splitinto two times before or after the upstream and downstream time slotssuch that it fits in the TDD frame.

11) This procedure may be repeated to assign off times to each line, oreach line may autonomously assign off times.

12) Set the times for the next slots, either internally or bycommunicating with external equipment. If the transceivers are externalto the management system, then the management system notifies thetransceivers of one or more of the future assignments: beginning of theupstream time slot(s), ending of the upstream time slot(s), duration ofthe upstream time slot(s), the beginning of the downstream time slot(s),ending of the downstream time slot(s), duration of the downstream timeslot(s), the beginning of the off time slot(s), ending of the off timeslot(s), duration of the off time slot(s),

The calculation of TDD slot times and off times may also be performed invarious other ways, by a direct calculation that maximizes theprojection of user demands on the achievable space, by iterativelyadjusting the slot boundaries from frame-to-frame, via heuristics, byselecting from among a stored set of timings, a generalized algorithmthat uses several of these approaches, etc. In addition, the framelength can be variable, the time slot start and end times need not beperiodic, and these need not be aligned. Frame lengths can be varied tomeet delay requirements, e.g., a short frame when low-delay applicationsare used. The calculation may simultaneously be applied to multiple TDDframes. All of this may be determined by the TDD management system.

The TDD management system may be made to be capable of convertinghigh-level requests for traffic and power consumption into low-level TDDscheduling. High-level requests may be e.g. an outline of traffic andpower requirements, or a general indication of the trade-off betweentraffic delay and power usage. The TDD management system may alsocoordinate power savings that are achieved by entering, exiting, ortransitioning between multiple power line states. In addition to TDD offtimes, these power line states can save power by transmitting a lowerbit rate with a lower bit loading using a lower transmit spectrum.

Part of each frame time may be reserved on a long-term basis for downand up time slots, with an additional part dynamically varied as trafficcomes and goes. The TDD management system then optimizes time slotassignment using both long-term and short-term variations.

TDD up and down time slots and the asymmetry ratio can be varied tominimize average traffic delays and maximize average throughput acrossall lines in the TDD group. The asymmetry ratio can be defined in termsof time for each slot or in terms of the number of DMT (DiscreteMulti-Tone) symbol positions used by a particular user in upstream ordownstream. Alternatively, the performance of some set of premiumservices can be maximized. As a further alternative, the worst-caseperformance can be maximized. As a further alternative, a more generalfairness criterion, such as “alpha-fairness” can be applied to maximizeany arbitrarily weighted combination of different user traffic demands.

The TU-Rs are often synchronized to the timing of the TU-O. This timingcan be assisted by regularly sending a “synch symbol” downstream thatthe TU-Rs can lock on to maintain a level of timing synchronization. TheTDD management system can determine the times to send synch symbols andthe synch symbol durations. When there is very little traffic, the linecould be off during an entire down or up time slot, or during an entireTDD frame, or even during multiple TDD frames. Then, the TDD managementsystem can schedule the VTU-O to send enough synch symbols, with enoughduration, so that the TU-R maintains or regains synchronization. Thesesynch symbols may be sent in only some time slots, in only some TDDframes, and even using only some subcarriers. The synch symbols can usea low-level modulation for robustness. This enables an inactive TU-R tomaintain TDD frame timing so that the TU-R can transmit during anupstream time slot when it wakes up.

A transceiver, such as a TU-R or TU-O may stay in receive-only mode,with the transmitter turned off. This allows power savings by turningoff the transmitter. In this mode, the transceiver may also listen toregularly-occurring receptions to maintain synchronization and to heartraffic or instructions to wake up.

An alternative wake-up procedure is for a TU-R to listen to the noise onthe line, and determine when there is NEXT by readingregularly-occurring high-power noise once every TDD frame or at anyother suitable interval. The TU-R transmits start-up signals when itestimates that this NEXT is active, which should be during an upstreamtime slot.

There may be a two step process for TU-R wake-up:

1: The TU-R stays approximately synchronized through slow periodic keepalives from the TU-O;

2: When the TU-R wants to start transmitting after some time period ofupstream and downstream inactivity (and hence synchronization is onlyapproximate):

-   -   a) The TU-R sends a short sync request in what it thinks is the        middle of the upstream frame period (sending the short message        in the middle ensures that the transmission is entirely within        the upstream period);    -   b) The TU-O responds with a transmission that the TU-R can use        for recovering synchronization;    -   c) Transmission proceeds normally.

Transmission systems adapt to the noise environment on the line, and thedescribed techniques may ensure that adaptation is performed whilecrosstalking lines are actively creating crosstalk and not during quiettimes.

Vectoring technology, as exemplified in the ITU-T G.993.5 standard, isused to cancel at least some FEXT. In order for vectoring to beeffective, if it is applied to a TDD group, NEXT should be kept low. Sothe avoidance of NEXT also allows vectoring to function better. Thedescribed techniques can coordinate the TDD timing with the vectoringengine. The TDD management system can reassign vectoring resources inreal-time when the TDD asymmetry ratio changes.

The TDD management system can also schedule when to send retransmissionunits. Retransmission units may be sent at any time. In someembodiments, retransmission units are sent at times that don't causeNEXT problems in a part of what would have been an off time, orretransmission units are sent with multiple retransmissions at otherframe times. Retransmissions can be incremental, with all or part of theoriginal data retransmitted, or by sending additional parity bits.Multiple retransmissions can be scheduled, and a block of original datacan be retransmitted in one or more blocks of data or parity.Acknowledgements (ACKs) or negative acknowledgements (NACKs) related toretransmission can also be scheduled by the invention.

The avoidance of NEXT between lines in a single TDD group is relativelystraight-forward compared to avoiding NEXT with multiple lines. The TDDcoordination simply needs to enforce this among the lines from a singleaccess node, which all originate in the same location and so arerelatively easy to jointly control.

FIG. 10 is a diagram of a more complex system implementation in whichthere are multiple TDD groups that have crosstalk coupling between someof their lines, for example between the two TDD groups in a Shared Cable3 in FIG. 10. In this case the TDD management may span multiple accessnodes, either explicitly with a centralized management element, orautonomously by detecting crosstalk.

Centralized TDD management allows multiple TDD groups to be coordinateddirectly. Centralized TDD management can use explicit timing informationand feedback from access nodes, EMS, or other network elements to thencentrally optimize all interacting TDD groups.

As shown in FIG. 10, centralized TDD management 111 may be coupledthrough a network 112 to multiple access nodes 113-1, 113-2. While onlytwo are shown, there may be many more. The centralized TDD managementreceives traffic data as described above, performs the assignments andthen sends time slot assignments to the access nodes. The access nodesare coupled through communications channels to one or more end nodes orTU-Rs 116-1, 116-2, 116-3, 116-4. The communications channels may be inthe form of twisted pair wiring 117-1, 117-2, 117-3, 117-4, or in anyother form and may be in one or more binders 115-1, 115-2, 115-3. Thebinders may be in the form of a shared multiple conductor cable withlines for four or for hundreds of channels.

FIG. 10 illustrates that two channels 117-1, 117-2 that initially are ina common binder or cable and that may generate cross-talk with eachother may later be separated and combined with other channels in otherbinders. As shown, the second twisted pair 117-2 is separated from thefirst twisted pair 117-1 and later combined with a third twisted pair117-3 in a third binder 115-3. These two lines now generate crosstalkwith each other. This third twisted pair originated with a second binder115-2. The second and third lines may also be routed to a common or todifferent end stations 116-2 116-3. The crosstalk generated at any onepoint between two nearby channels may propagate along any one channeland affect other channels. As an example, the crosstalk generated by thefirst line 117-1 and received by the second line 117-2 may be coupled tothe third line 117-3 in the third shared cable. The third line 117-3 maycouple that same crosstalk from the first line 117-1 into a fourth line117-4.

The connections between lines in different cables or binders may occurin switches, junctions, crossboxes, distribution frames, pedestals, orother types of terminals including network-end terminal, such as TU-R's,or in splice points. In these locations channels can be separated fromtheir original binders and then recombined into different binders orcombined at a termination point. TDD systems may alternately not beassigned to separate binders at all, in which case crosstalk willusually arise between them resulting in essentially the sameconfiguration as in FIG. 10.

Autonomous TDD management 114-1, 114-2 at each access node 113-1, 113-2or at any other point in the system can coordinate multiple TDD groupseven though it reads data from, and controls, only a single TDD group.Synchronization may also be performed by measuring the time series oftime-varying crosstalk and synchronizing to its patterns. As anotheralternative, synchronization is performed by measuring the time seriesof error events and synchronizing to its patterns. This may be done byreading in the time-varying pattern of noise or errors on the lines inthe TDD group. Crosstalk from another “alien” TDD system, such as thatfrom a different access node, creates a regularly-occurring pattern ofnoise as it alternately transmits in both directions, first in onedirection, then in the other. This crosstalk can be measured by readingthe noise on the lines, or by reading the time-series of error patterns.These can be analyzed on both ends of the line to identify the patternof the alien TDD groups' up and down time slots. For example, errorsoccurring in one direction once each millisecond indicate that crosstalkis being generated once each millisecond from the alien TDD groups. TheTDD management system can then synchronize its own transmissions to thiscrosstalk.

FIGS. 3, 7, and 10 all show different perspectives of the samecommunication system. While the time slot assignment may be performed atany of a variety of different locations, in each case, the transmissionsare either controlled directly or the controller sends assignments tothe appropriate transmitter. The assignments may be sent, e.g., to atransceiver unit (TU), to a crossbox, to a switch, to a junction, to apedestal or to another type of transmitter whether it is an originalsignal source or a repeater at any point in the channel. Similarly, thecontroller can provide synchronization signals that allow the upstreamand downstream signals to be coordinated. Synchronization can also bebased on signals from a vectoring unit, from an access node, a crossbox,or some other junction point or from an external clock orsynchronization source. In one example, synchronization symbols are sentto the sources of upstream transmissions, such as TU-R's.

TDD management may more generally be split between centralized andautonomous methods, using traffic data and TDD synchronizationinformation from:

a) Explicit use of management data and synchronization data from DSLAMs,EMS, OSS or other network elements;

b) Global synchronization data using Global Positioning Satellite (GPS)data or network timing protocols;

c) Autonomous estimation using monitoring data on crosstalk patterns orby reading time-varying noise or error counts;

d) Explicit estimates of crosstalk couplings between lines can be input,for example vectored lines can provide such data as reported Xlinvalues.

The TDD management system may adjust one or more of the followingquantities or other quantities not listed for one or more lines:

a) asymmetry ratio,

b) up and down slot times,

c) off times; and

d) use of low-power or quiescent states;

with the objective of meeting bit-rate requirements and requests, andoptionally minimizing power. These can also be set indirectly throughhigher-level or lower-level control specifications. These can becontrolled by slowly changing them as scheduled or as needed after atraffic threshold is crossed; or they can vary in real time. DynamicBandwidth Allocation (DBA) or Dynamic Resource Allocation (DRA) can alsobe all or part of this control. The TDD management system may alsointerface with, or contain, a Timing Control Entity (TCE).

The TDD management system's capability to detect and adapt to TDDcrosstalk can assist in enabling spectral compatibility of TDD systemswith FDM (Frequency Division Multiplexed) systems such as VDSL2 (Veryhigh bit rate Digital Subscriber Line, version 2). This can be done byusing automated crosstalk identification, coordinating TDD timings, andDynamic Spectrum Management (DSM) to enable the TDD system to becompatible with VDSL2. Frequency band assignments may further becoordinated to enable spectral compatibility.

FIG. 11 is a process flow diagram of scheduling upstream and downstreamtime slots according to another embodiment. The process flow isspecifically intended for use in managing multiple time divisionphysical channels that are subject to crosstalk, however, the inventionis not so limited. The scheduling is described here in the context oftwo physical channels that are subject to crosstalk, however there maybe many more than two channels.

At 1104, the TDD management system receives input about trafficobjectives for the scheduling of the time slots. This operation isoptional. The input is typically received from an external controller,although the TDD management system may be able to monitor the channelsor use preset parameters instead of any received input. In a typical DSLsystem external controllers already generate Operations Support System(OSS) data and Management Information Database (MIB) parameters. Thisinformation may be provided to the TDD management system for it use inassigning time slots. Other types of information may also be used. Thereceived input may be of a variety of different types and may includedesired traffic levels, static subscription data, service layerinformation from a policy manager, behavior data for traffic types andusers of the physical channels, long term traffic behavior data as afunction of time, current traffic demands, queue lengths, trafficrequests, upstream/downstream asymmetry, and traffic descriptors. Thereceived input may also include transmission requests from networkelements at the network end or the remote end.

At 1106, the TDD management system schedules upstream time slots forupstream transmission in one or more physical channels. AT 1108, the TDDmanagement system schedules downstream time slots for downstreamtransmission in one or more physical channels. This may be the samechannels as the upstream channels or different channels, depending onthe nature of the TDD system and the assignment of channels. Theupstream channels may be assigned before or after or at the same time asthe downstream channels. In these assignments transmission in theupstream time slots is substantially not simultaneous with transmissionin the downstream time slots. To make these assignments, all or some ofvarious types of information in the received input can be used. Thesecan be combined in different ways. In one example, optimization criteriaare used that weigh different factors.

There are additional factors that may also be considered in thescheduling such as power usage, or a target upstream/downstreamasymmetry ratio of data throughput. The data throughput can be definedor measured as an average throughput across all lines, a traffic demandmatch, a minimum throughput for each physical channel, a perceivedquality of experience, an average delay, or a minimum delay.

As mentioned previously, the scheduling may allow some simultaneoustransmission in the upstream and downstream time slots. The NEXT thatmay be caused by the simultaneous transmission may be ignored or the TDDsystem may also use active NEXT cancellation to cancel NEXT at thenetwork end of the channels.

As a part of the scheduling, the TDD management system will typicallysend time slot assignments to a corresponding network element. At 1110,the TDD management system may also optionally synchronize times slotamong different transmitters. The TDD management system may send synchsymbols to source of upstream or downstream transmissions. It may alsomeasure a time series of time-varying crosstalk and then synchronize thetime slots to the measured time-varying patterns. Instead of crosstalkpatterns, a time series of error events may be measured and used tosynchronize.

At 1112, the TDD management system may optionally adjust the schedulingof upstream and downstream time slots. The adjustment may be applied tothe next frame or frames, or to the current assignments. The adjustmentmay accommodate delay requirements for an upstream or downstream trafficsource. Many different adjustments may be made such as moving theupstream and downstream time slots in time to reduce simultaneousupstream and downstream transmission, moving only if upstreamtransmissions overlap downstream transmissions in time, and reducing theduration of at least one downstream time slot to reduce simultaneousupstream and downstream transmission.

FIG. 12 is a block diagram of a TDD management system 1200 in oneexample. The system 1200 includes a memory 1295 coupled directly orthrough a bus to a processor or processors 1296. The memory may be ahard drive, non-volatile memory, solid state memory, or a combination ofdifferent memory types for different purposes. The processor may alsoinclude its own internal memory. The memory may, for example, storeinstructions to be executed and the processor may execute the storedinstructions. The processor may also implement or execute implementinglogic 1260 having logic to implement the methodologies discussed herein.System 1200 includes one or more communications buses 1215 to connectthe various illustrated components and to transfer transactions,instructions, requests, and data within the system among the componentsand other peripheral devices. The system further includes a managementinterface 1225 coupled to the bus and to external management devices,for example, to receive requests, return responses, and otherwiseinterface with network elements located separately from the system. Thisinformation may include Operations Support System (OSS) data andManagement Information Database (MIB) parameters. These network elementsmay include access nodes, a central office, vectoring units, crossboxes,TU-Rs, and TU-Os.

The system further includes a LAN (Local Area Network) interface 1230coupled to the bus and externally to communicate information via a LANbased connection, including collecting network information, reportinginformation and diagnostics to other entities within the network, andfor initiating instructions and commands over the network. The systemfurther includes a WAN (Wide Area Network) interface 1235 coupled to thebus and to an external WAN, to communicate information via a WAN basedconnection for similar purposes and to reach other more remote devices.

In some embodiments, the management interface 1225 communicatesinformation via an out-of-band connection separate from LAN and/or WANbased communications, where “in-band” communications are communicationsthat traverse the same communication means as payload data (e.g.,content) being exchanged between networked devices and where“out-of-band” communications are communications that traverse anisolated communication means, separate from the mechanism forcommunicating the payload data. An out-of-band connection may serve as aredundant or backup interface over which to communicate control databetween a management device 1201 and other networked devices or betweenthe management device and a third party service provider.

The system further includes stored historical information 1250 which maybe stored within the memory 1295 or as a separate component coupled tothe memory or to the bus. The historical information may be analyzed orreferenced when conducting long term trending analysis for schedulingtime slots and for reporting. Similarly management events 1255 may bestored within the memory or as a separate component coupled to the busor to the memory. The management events may be initiated responsive tothe identification of an operational condition. For example, correctiveactions, additional diagnostics, information probes, configurationchange requests, local commands, remote execution commands, and the likemay be specified by and triggered as a management event 1255. Similarly,operational reports, configuration reports, network activity reports anddiagnostic reports may be generated and sent in accordance with storedmanagement events 1255.

A management device 1201 coupled to the bus includes a collection module1270, analysis module 1275, diagnostics module 1280, and implementationmodule 1285. Management Device 1201 may be installed and configured in acompatible system 1200 as is depicted by FIG. 12A, or providedseparately so as to operate in conjunction with appropriate implementinglogic 1260 or other software.

The collection module 1270 collects information from available sources,such as management information, LAN information and WAN information viathe external interfaces. The scheduling module 1275 analyzes theinformation retrieved by the collection module and generates upstreamand downstream time slot schedules including, as appropriate, off timesand active transmission times. The scheduling module may further performlong term trending analysis based on stored historical information 1250or conduct neighborhood analysis based on aggregation data yielded frommultiple separate and distinct reports, or conduct other joint analysisbased on collected information. The adjusting module 1280 adjusts theschedules to better suit the collected information and internalparameters, such as power usage and asymmetry ratio objectives. Theresults from the adjusting module may be supplied back to the schedulingmodule, depending on the embodiment. The synchronizing module 1285synchronizes the scheduled time slots through the external connections1225, 1230, 1235 so that all of the access nodes, transmitting units, orother components transmit at appropriate times.

The modules of the management device 1201 may be provided as separatecomponents coupled to the bus 1215 as shown or may be incorporated intothe processor or memory or another component. The management device mayinclude its own processing and memory resources that interact with theprocessor and the external interfaces. The management device may includemore or fewer modules than those shown. The TDD management system ofFIG. 12 is provided only as an example and may be modified to suitdifferent implementations. It may also be incorporated into anothercomponent such as an access node, or a TU-O. In one embodiment, themanagement system is provided as a card in a system rack with abackplane interface to communicate with local and remote networkelements.

There are a number of optional and additional advantages and features tothe described techniques and systems above. These can be understood inthe statements below, among others which may be combined in any of avariety of different ways.

A system has been described above for managing multiple TDD lines, inpart, by determining time slot boundaries. The system providessufficient coordination to avoid NEXT by ensuring that two lines withsignificant crosstalk coupling do not transmit downstream and upstreamat the same time. The system further assigns slot-times and thedownstream/upstream asymmetry ratio to maximize a measure of throughput.The maximized measure of throughput is one or more of: the maximumaverage or minimum average across all lines; chosen to best matchtraffic demands; chosen to provide a minimum service level to all lines;chosen to ensure user-perceived quality of experience; chosen tominimize average or maximum delays; or chosen to meet any fairnesscriteria. Other measures of throughput may be used as alternatives oradditions, depending on the implementation. The assignment of time slotsmay be internal to a transceiver, or it may be transmitted from the TDDmanagement system into a transceiver. The TDD management system canfurther perform Dynamic Bandwidth Allocation (DBA) or Dynamic ResourceAllocation (DRA).

The TDD management system can further optimize the scheduling of offtime slots to minimize power usage. The TDD management system canfurther schedule off times during low traffic that suppress transmissionfor the duration of entire time slot, TDD-frame, or multiple TDD frames.It may save power by controlling entries, exits, and transitions betweenlow-power states. Low-power states save power by transmitting a lowerbit rate with a lower bit-loading using a lower transmit spectrum.

The TDD management system can calculate an optimal set of up and downslot times and off times according to an optimization criteria, thiscriteria can flexibly weigh different tradeoffs between different users,tradeoffs between different services, and tradeoffs between performanceand power savings.

The TDD management system adjusts one or more of the following or otherquantities for one or more lines: a) asymmetry ratio, b) up and downslot durations, c) up and down slot times, and d) off times. The TDDmanagement system controls the TDD time slot boundaries and off times.This can be a fixed assignment, a slowly varying assignment based ontime-of-day, or an assignment that is varied in real time. One or morecontrol parameters such as any one slot time start or end point, slotlengths, asymmetry, up slot time, down slot time, a single off time, andtotal off time, can be varied while other parameters remain fixed. TheTDD management system may employ flexible slot-time boundaries, withvariable-length frames, up slot-times, and down slot-times.

The TDD management system receives input on the traffic levels that needto be provided on the lines under its control. This input may includeone or more of the following: static (time-invariant) data about servicesubscription levels and their traffic requirements; service layerinformation from a policy manager which provides high-level estimates ofdata rate requirements based on service requests; data on the behaviorof different traffic types e.g., burstiness, for different users;time-series data from long-term traffic monitoring which is analyzed todetermine the traffic demands as a function of time-of-day ortime-of-week; instantaneous feedback based on current traffic demands orqueue lengths; and traffic requests or reports sent from the customerend.

The TDD management system can be further controlled by externalOperations Support Systems (OSS) or by reading and writing ManagementInformation Database (MIB) parameters. A single TDD group can be managedor multiple TDD groups can be managed. The TDD management system may bea centralized controller that controls multiple lines, and/or multipleTDD groups. Alternatively, the TDD management system may be distributedamong multiple pieces of equipment.

The TDD management system can control synchronization of a TDD group.This synchronization can be assisted by using one or more of thefollowing input data: explicit use of management data andsynchronization data from DSLAMs, EMS (Element Management Systems), OSS(Operations Support Systems) or other network elements; globalsynchronization data using Global Positioning Satellite (GPS) data ornetwork timing protocols; autonomous estimation reading time-varyingnoise that contains crosstalk patterns or by using monitoring data suchas error counts.

The timing reference can be further used to control the synchronizationof multiple TDD groups. The TDD management system can provideinformation to assist the synchronization of multiple lines and/ormultiple TDD groups.

The TDD management system can determine the times to send synch symbolsand the synch symbol durations. The TDD management system can schedulethe VTU-O to send synch symbols sufficiently often and with sufficientduration, for the VTU-R(s) to maintain synchronization with the VTU-O.These synch symbols may be sent only in some time slots, in some TDDframes, and only using some subcarriers. The synch symbols can use alow-level modulation for robustness. Long synch symbols can be scheduledto be sent from the VTU-O to recover synchronization after long offtimes. The TDD management system may further coordinate off times byinstructing one or more transceiver(s) to be in receive-only mode, withthe transmitter turned off for some time period, or until it receives asignal, or until traffic in a queue crosses a threshold.

An inactive TU-R can listen to the noise on the line, and determine whenthere is NEXT by reading regularly-occurring high-power noise once everyTDD frame. The TU-R then transmits start-up signals when it estimatesthat this NEXT is active, which should be during an upstream time slot.

The TDD management system may use multiple, distributed components, eachoperating autonomously. The autonomous TDD system can further read incrosstalk coupling data. The crosstalk data can be used to determinewhich TDD groups and which lines to coordinate. A combination ofcentralized and autonomous TDD management can be supported.

The TDD management system can further control FEXT cancellation using,for example, vectoring. Vectoring resources can be re-assigned inreal-time when the TDD asymmetry ratio changes. The TDD managementsystem can adapt to satisfy varying delay requirements for differentlines, subscribers, services, and at different times. The TDD managementsystem can assist compatibility with FDM systems (e.g., G.fast andVDSL2), use crosstalk identification and “fingerprinting” of FDM and TDDcrosstalk. The TDD management system can control retransmission, assignretransmission time slots, coordinate Hybrid retransmission that canre-send multiple parts of a block of data and/or multiple parity bits.

The TDD management system can manage allocation of time slots foracknowledgement messages (ACKs) and/or negative acknowledgement messages(NACKs). The TDD management system can further coordinate TDD groupsthat have NEXT cancellation or partial NEXT cancellation, therebyallowing some overlap between down and up time slots that have suchcancellation.

In this description, numerous specific details such as logicimplementations, opcodes, means to specify operands, resourcepartitioning/sharing/duplication implementations, types andinterrelationships of system components, and logicpartitioning/integration choices are set forth. It will be appreciated,however, by one skilled in the art that the different implementationsmay be practiced without such specific details. In other instances,control structures, gate level circuits and full software instructionsequences have not been shown in detail in order not to obscure thedescription.

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to effect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

In this description and claims, the terms “coupled” and “connected,”along with their derivatives, may be used. It should be understood thatthese terms are not intended as synonyms for each other. “Coupled” isused to indicate that two or more elements, which may or may not be indirect physical or electrical contact with each other, co-operate orinteract with each other. “Connected” is used to indicate theestablishment of communication between two or more elements that arecoupled with each other. The operations of the flow and signalingdiagrams are described with reference to exemplary embodiments. However,it should be understood that the operations of the flow diagrams can beperformed by variations other than those discussed with reference tothese other diagrams, and the variations discussed with reference tothese other diagrams can perform operations different than thosediscussed with reference to the flow diagrams.

As described herein, instructions may refer to specific configurationsof hardware such as application specific integrated circuits (ASICs)configured to perform certain operations or having a predeterminedfunctionality or software instructions stored in memory embodied in anon-transitory computer readable medium. Thus, the techniques shown inthe figures can be implemented using code and data stored and executedon one or more electronic devices (e.g., a UE, an eNB, etc.). Suchelectronic devices store and communicate (internally and/or with otherelectronic devices over a network) code and data using machine-readablemedia, such as non-transitory machine-readable storage media (e.g.,magnetic disks; optical disks; random access memory; read only memory;flash memory devices; phase-change memory) and transitorymachine-readable communication media (e.g., electrical, optical,acoustical or other form of propagated signals—such as carrier waves,infrared signals, digital signals, etc.).

In addition, such electronic devices typically include a set of one ormore processors coupled to one or more other components, such as one ormore storage devices (non-transitory machine-readable storage media),user input/output devices (e.g., a keyboard, a touchscreen, and/or adisplay), and network connections. The coupling of the set of processorsand other components is typically through one or more busses and bridges(also termed as bus controllers). Thus, the storage device of a givenelectronic device typically stores code and/or data for execution on theset of one or more processors of that electronic device. Of course, oneor more parts of an embodiment of the invention may be implemented usingdifferent combinations of software, firmware, and/or hardware

While the flow diagrams in the figures show a particular order ofoperations performed by certain embodiments of the invention, it shouldbe understood that such order is exemplary (e.g., alternativeembodiments may perform the operations in a different order,

While the invention has been described in terms of several embodiments,those skilled in the art will recognize that the invention is notlimited to the embodiments described, can be practiced with modificationand alteration. The description is thus to be regarded as illustrativeinstead of limiting.

1. A method in a data communications system for managing multiple timedivision physical channels that are subject to crosstalk, the methodcomprising scheduling upstream time slots for upstream transmission in afirst physical channel; and scheduling downstream time slots fordownstream transmission in a second physical channel, whereintransmission in the upstream time slots is substantially notsimultaneous with transmission in the downstream time slots.
 2. Themethod of claim 1, wherein scheduling downstream time slots comprisesallowing some simultaneous transmission in the upstream and downstreamtime slots, the method further comprising cancelling near-end crosstalk(NEXT) from downstream into upstream transmission at a network end ofthe channels.
 3. The method of claim 1, wherein the upstream anddownstream time slots have an active portion during which signals aretransmitted and an off portion during which no signals are transmittedand wherein the active portions of the upstream time slots aresubstantially not simultaneous with the active portions of thedownstream time slots.
 4. The method of claim 1, wherein schedulingupstream and downstream time slots comprises scheduling upstream anddownstream time slot boundaries.
 5. The method of claim 4, wherein thetime slot boundaries are flexible.
 6. The method of claim 5, wherein thetime slot boundaries have one or more of: variable-length frames;variable upstream time slot lengths; and variable downstream timeslot-lengths.
 7. The method of claim 1, further comprising assigningtime slots to a network element based on the scheduling and transmittingthe assignments from a management system to a network element.
 8. Themethod of claim 1, further comprising adapting scheduling at least oneof upstream and downstream time slots to accommodate delay requirementsfor the other of a downstream and upstream traffic source.
 9. The methodof claim 1, further comprising receiving input on desired traffic levelsfor the first and second physical channels and wherein schedulingupstream and downstream time slots is performed based on the receivedinput.
 10. The method of claim 9, wherein a portion of a downstream timeslot is invariant and a portion of a downstream time slot varies inreal-time.
 11. The method of claim 9, wherein the received inputcomprises at least one of static subscription data, service layerinformation from a policy manager, behavior data for traffic types andusers of the physical channels, long term traffic behavior data as afunction of time, current traffic demands, queue lengths, trafficrequests, upstream/downstream asymmetry, and traffic descriptors. 12.The method of claim 9, wherein scheduling upstream and downstream timeslots comprises assigning time slots to achieve a targetupstream/downstream asymmetry ratio of data throughput.
 13. The methodof claim 12, wherein the upstream/downstream asymmetry ratio is definedin numbers of discrete multi-tone symbol positions.
 14. The method ofclaim 12, wherein the measure of throughput is at least one of anaverage throughput across all lines, a traffic demand match, a minimumthroughput for each physical channel, a perceived quality of experience,an average delay, and a minimum delay.
 15. The method of claim 1,wherein scheduling upstream and downstream time slots comprisesassigning time slots based at least in part on power usage.
 16. Themethod of claim 15, wherein assigning time slots based on power usagecomprises assigning by scheduling entries, exits, and transitionsbetween low-power link states and off states.
 17. The method of claim15, wherein assigning time slots based on power usage includes assigningat least one network element to a receive-only mode, with a transmitterof the network element turned off.
 18. The method of claim 10, whereinscheduling upstream and downstream time slots comprises assigning timeslots using an optimization criteria that weights different factors. 19.The method of claim 18, wherein receiving input comprises receivinginput from an external controller.
 20. The method of claim 19, whereinthe received input comprises at least one of Operations Support System(OSS) data, Element Management System (EMS) data, and ManagementInformation Database (MIB) parameters.
 21. The method of claim 10,wherein the time slots are defined within a time division frame, whereinreceiving input comprises receiving input during a frame, and whereinscheduling upstream and downstream time slots comprises schedulingupstream and downstream time slots of an immediately subsequent frame.22. The method of claim 1, further comprising receiving requests forupstream and downstream transmission and wherein scheduling upstreamtime slots is based on the received upstream transmission requests. 23.The method of claim 1, wherein the transmission in the upstream timeslots is from a plurality of different network-end transmission sources.24. The method of claim 23, further comprising synchronizing upstreamtransmission and downstream transmission among a plurality of differentnetwork-end transmission sources.
 25. The method of claim 24, whereinsynchronizing comprises sending synch symbols to a source of upstreamtransmissions.
 26. The method of claim 24, wherein synchronizingcomprises measuring a time series of time-varying crosstalk andsynchronizing to time-varying patterns of the crosstalk.
 27. The methodof claim 24, wherein synchronizing is performed by measuring a timeseries of error events and synchronizing to time-varying patterns of theerror events.
 28. The method of claim 1, wherein scheduling upstream anddownstream time slots comprises determining a duration of the upstreamand downstream time slots and moving the upstream and downstream timeslot start times to reduce simultaneous upstream and downstreamtransmission.
 29. The method of claim 28, wherein determining a durationcomprises adjusting a default duration based on bandwidth requests. 30.The method of claim 28, wherein moving comprises moving only if upstreamtransmissions overlap downstream transmissions in time.
 31. The methodof claim 28, further comprising reducing the duration of at least onedownstream time slot to reduce simultaneous upstream and downstreamtransmission.
 32. The method of claim 1, wherein the scheduling upstreamand downstream time slot is further performed to minimize crosstalk onnearby VDSL2 lines.
 33. The method of claim 1, further comprisingreceiving input on desired traffic levels for the first and secondphysical channels and wherein scheduling upstream and downstream timeslots is performed based on the received input and at least in part onpower usage.
 34. A machine-readable medium having instructions that whenoperated on by the machine cause the machine to perform operationscomprising: scheduling upstream time slots for upstream transmission ina first physical channel of multiple time division physical channels ina data communication system in which the physical channels are subjectto crosstalk; and scheduling downstream time slots for downstreamtransmission in a second physical channel subject to crosstalk from theupstream time slots, wherein transmission in the upstream time slots issubstantially not simultaneous with transmission in the downstream timeslots.
 35. The medium of claim 34, the operations further comprisingreceiving input on desired traffic levels for the first and secondphysical channels and wherein scheduling upstream and downstream timeslots is performed based on the received input.
 36. The medium of claim34, wherein scheduling upstream and downstream time slots comprisesassigning time slots to achieve a target upstream/downstream asymmetryratio of data throughput.
 37. An apparatus for managing multiple timedivision physical channels in a data communications system that aresubject to crosstalk, the apparatus comprising means for schedulingupstream time slots for upstream transmission in a first physicalchannel; and means for scheduling downstream time slots for downstreamtransmission in a second physical channel subject to crosstalk from theupstream time slots, wherein transmission in the upstream time slots issubstantially not simultaneous with transmission in the downstream timeslots.
 38. The apparatus of claim 37, further comprising means forassigning at least one network element to a receive-only mode, with atransmitter of the network element turned off.
 39. The apparatus ofclaim 37, further comprising means for receiving requests for upstreamand downstream transmission for use by the means for scheduling.
 40. Asystem with multiple physical channels in a data communications systemtransmitting point-to-multipoint over multiple copper wires that aresubject to crosstalk, wherein the system allows full-duplex operation byusing line hybrids and echo cancellation to separate upstreamtransmission from downstream transmission, and near-end crosstalk (NEXT)is cancelled only at the network-end of the channels, from downstreaminto upstream transmission, wherein transmission in the upstream timeslots may occur simultaneous with transmission in the downstream timeslots.